The present invention relates generally to a device for sensing changes in temperature at a given point and more particularly to a temperature transducer which is particularly suitable for sensing temperature change in electrical transmission and distribution equipment or at other such locations where strong electric and/or magnetic fields are present or where the presence of metal is undesirable.
Heretofore, it has been common practice to monitor the temperature at particular points within an operating transformer by direct measurement, that is, by sensing the temperature directly at or in close proximity to the coils and/or core of the transformer. This has primarily been due to the fact that most monitoring devices utilized in the past included metal sensors and/or wires and that such sensors and/or wires located within the transformer could adversely effect the electric field distribution therein. This, in turn, could possibly lead to arcing and transformer failure. In order to avoid this type of problem, calculational schemes involving the top oil temperature of the transformer as a parameter have generally been employed to compute the temperature rise within its core and coils. However, experimental verification of this method has not been generally possible and hence it is not known whether this type of indirect measurement adequately reflects the temperatures at the desired points within the transformer.
More recently, semiconductor transducer/electronic modules and differential dielectric expansion devices have been investigated for direct coil temperature measurement. However, these semiconductor devices have met with only limited success because of their change in function at high temperature and because of their relatively large size.
As will be seen hereinafter, the temperature sensing device of the present invention is one which can monitor directly and accurately the temperature at a desired point within a transformer or similar equipment, even at high temperatures, without disturbing the electric or magnetic fields therein. As will also be seen, this device is one which is uncomplicated in design, relatively small in size, easy to manipulate and inexpensive to manufacture.